Virtual LED Clock For Windows By Trent Jackson

[T.Jackson]

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Not your ordinary Windows-based desktop clock, this one's PIC-driven! Yes that's right, the Windows software is just a display, it's the PIC that actually keeps the time. The circuit connects to any spare serial port on your PC and feeds the Windows-based software with an accurate time string every second. Setting the time is snack, this is done directly via the Windows software. The time can be set or displayed in either 12 or 24 hour formats.

An interesting aspect of this project is that, in the Windows software, instead of using MSCOMM32.ocx, it uses a relatively much easier-to-use API based approach. First initial tests with this protocol have proven flawless. I haven't confirmed this yet but I think it might actually be much faster too. So for Windows developers out there using VB, I strongly suggest that you take a close look at the protocol in the download.

Anyhow, turning your attention back to the clock for a moment, if you take a look at the schematic below you'll see that the whole thing can be built for less than the cost of your lunch. The circuit relies on no dedicated RTC chip, but instead uses portions of Paul R. Borgmeier's EZCLOCK2 code which makes good use of TMR0 to enable for some relatively accurate time keeping. Arguably almost on par with the DS1302. Last but not least, some of you may be asking what's the buzzer and LED for? Well, as it stands with the software "as is", the buzzer briefly goes off every second making a sort of tick-tock sound.
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Schematic
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'******************************************************************************
'*   Name    : VClock.BAS                                                     *
'*   Author  : Trent Jackson                                                  *
'*   Notice  : No Copyright                                                   *
'*           :                                                                *
'*   Date    : 17/5/2007                                                      *
'*   Version : 1.0                                                            *
'*                                                                            *
'* Acknowledgements                                                           *
'* Portions of Program extracted from: EZCLOCK2 By Paul R. Borgmeier, PhD     *
'* Crux analysis & design, LLC www.cruxanalysis.com                           * 
'******************************************************************************

   Include "modedefs.bas"             ' Serial Protocol
   Define   OSC 4                     ' 4MHz crystal used
                                      '
   '// Variables
   Counter    VAR Word                ' Track TMRO  
   Hours      VAR Byte                ' Total hrs (0-23)
   Minutes    VAR ByTE                ' Mins (0-59)
   Seconds    VAR Byte                ' Secs (0-59)
   RX_To_PC   VAR PORTA.0             ' RX line
   TX_To_PC   VAR PORTA.1             ' TX ...
   LED_Buzzer VAR PORTB.5             ' LED & Buzzer
   
   '// Init
   CMCON       = 7                    ' All digital
   OPTION_REG  = %10000111            ' TMRO prescale = 256
   TRISA       = %00000010            ' All outputs except RA1
   TRISB       = %00000000            ' All outputs ...
   TMR0        = 0                    ' Reset TMRO
   INTCON.2    = 0                    ' Clear TMRO overflow flag
   Hours       = 0                    ' Null  
   Minutes     = 0                    ' ^
   Seconds     = 0                    ' ^
   Counter     = $7A12                ' Load time counter
   
   '=============
   Wait_For_TMR0:                     ' Main loop  
   '=============
   IF INTCON.2 = 0 THEN Wait_For_TMR0 ' Wait for TMRO overflow
   INTCON.2    = 0                    ' Clear TMRO overflow flag
       Counter = Counter - $800       ' Dec counter until 1 sec has elapsed  

   '// Process hrs, mins secs accordingly ...
   IF Counter < $800 THEN
      Seconds = Seconds + 1
      If Seconds = 60 Then
         Seconds = 0
         Minutes = Minutes + 1
         If Minutes = 60 Then
            Minutes = 0
            Hours = Hours + 1
            If Hours = 24 Then
               Hours = 0
            EndIf
         EndIf
      EndIf
   
   '// Add leading zeros to all single digits & output str serially to PC
      If Hours < 10 And Minutes > 9 And Seconds > 9 Then
         SEROUT RX_To_PC, N2400, ["@","0",#Hours,":",#Minutes,":",#Seconds]
      ELSE:IF Hours > 9 and Minutes < 10 and Seconds > 9 THEN
         SEROUT RX_To_PC, N2400, ["@",#Hours,":0",#Minutes,":",#Seconds]
      ELSE:IF Hours < 10 and Minutes < 10 and Seconds > 9 THEN
         SEROUT RX_To_PC, N2400, ["@","0",#Hours,":0",#Minutes,":",#Seconds]
      ELSE:IF Hours > 9 and Minutes > 9 and Seconds < 10 THEN
         SEROUT RX_To_PC, N2400, ["@",#Hours,":",#Minutes,":0",#Seconds]
      ELSE:IF Hours < 10 and Minutes > 9 and Seconds < 10 THEN
         SEROUT RX_To_PC, N2400, ["@","0",#Hours,":",#Minutes,":0",#Seconds]
      ELSE:IF Hours > 9 and Minutes < 10 and Seconds < 10 THEN
         SEROUT RX_To_PC, N2400, ["@",#Hours,":0",#Minutes,":0",#Seconds]
      ELSE:IF Hours < 10 and Minutes < 10 and Seconds < 10 THEN
         SEROUT RX_To_PC, N2400, ["@","0",#Hours,":0",#Minutes,":0",#Seconds]
      Else
         SEROUT RX_To_PC, N2400, ["@",#Hours,":",#Minutes,":",#Seconds]
      EndIf: EndIf: EndIf: EndIf: EndIf: EndIf: EndIf

      Counter = Counter + $7A12          ' Reset counter 
      Toggle LED_Buzzer                  '  
   '//
   Else 'Wait here for 50mS to see if the host(PC) is trying to set new time val                               
   '//
      SERIN TX_To_PC, N2400, 50, Wait_For_TMR0, ["@"], Hours, Minutes, Seconds
   EndIf
   GoTo Wait_For_TMR0                    ' Loop back
   end

If you plan on running the Windows executable you'll firstly need to obtain msvbvm50.dll <a href="http://www.dll-files.com/dllindex/dll-files.shtml?msvbvm50" target="_blank">Click here!</a>.
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Happy time keeping !
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Trent Jackson
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